Sean O'Neill jumped out of his battered 1970s VW campervan and hit the tarmac with a determined thud. "Just wanted to take stock a bit before we descend on the masses," said the Dublin bank clerk, 29, pulling on a cigarette in a layby on the outskirts of Poznan.

Behind him lay a 2,000km drive from Ireland, for which he took the benefit of free petrol laid on by a bookmaker on Ushers Quay in Dublin, before boarding the ferry to Cherbourg. Though he thinks he will abandon the patched-up vehicle by the close of the tournament – until recently it was rusting in his parents' backyard – and take the plane back home, Sean says the journey will have been worth every mile, however slow and spluttering.

"There is nothing, simply nothing, like being able to travel across Europe to see the boys in green. Last time Ireland appeared at a European championship [in 1988], I was too young to remember much about it, so when we qualified this time round, I was like, 'Right, can't miss out on this opportunity'," he said.

It's also been 10 years since Ireland's appearance at any major tournament (the 2002 World Cup) and the "green army" is making up for it in style. Before Ireland's first Euro 2012 match against Croatia on Sunday, the travelling circus of fans were arriving in Poland in their thousands in every type of vehicle, from planes and trains to campervans in various states of disrepair – including a decommissioned ambulance and a caravan welded to a Ford Transit. Some have even arrived on bicycles. Up to 30,000 Irish fans are expected, meaning that Ireland, the second-smallest nation competing in the tournament, will be by far the best supported, barring the hosts.

Already, by Friday, Poznan – Poland's fifth largest city and the stage for a good portion of the Euro action – was heaving with Irish fans sipping beer and befriending the locals in the clammy summer heat.

As they gathered in bars on the central Stary Rynek square in front of Poznan's elegantly decorated sgraffito facades, in cafés on side streets off the old town district and on camping sites set up for the event, their green T-shirts and additional props and banners ensured they stood out. Some donned glitzy shamrock antennae, or curly wigs in the shades of the Irish tricolour, while others wore T-shirts with the slogan "In Trap We Trust", a tribute to the national team's beloved coach, Giovanni Trapattoni, perhaps the most popular Italian in Ireland since Padre Pio after his work in reinvigorating Ireland's football fortunes.

"The colour of the city has completely changed in the last few days," said Krzysztof Grobelny from the Poznan tourist information centre. "Normally it's defined by blue [the dominant colour of its Saints Peter and Paul coat of arms], but now it's a sea of white, orange, green, and red," he says, also referring to the Polish colours of red and white.

Emphasising what the people of both countries refer to repeatedly as their "special relationship", are the Polish bars and radio stations that make a point of pumping out songs like the rock ballad Kocham cie jak Irlandie ("I love you like Ireland"), by the band Kobranocka, Ajrisz ("Irish") by T-Love or Irlandie Zielona ("Green Ireland") by the electronic musician Kowalski. There are even some Poznan bars that seem to have turned into "Irish pubs" overnight.

The Polish effort has certainly not gone unnoticed by the Irish, veterans themselves of dishing out céad míle fáilte at every opportunity, who respond by painting the Polish flag on their faces.

"I heard they're putting on a special mass for the Irish fans on Sunday ahead of the Irish-Croatia game," said Francis Murtagh, 30, an accounts assistant at a Dublin insurance broker, who had arrived in Poznan on Friday on a €480 Ryanair flight. "Let's say if the sun's out and I'm nursing a pint, I don't suppose I'll be there myself, but there's no denying it's a lovely gesture and typical of the welcome we've received so far."

His friend Mark Bergin, 30, a senior associate of reconciliations and cash management for a financial company, admitted a major motivating factor in coming to the championship was the opportunity to escape from Ireland's economic woes. "It's a chance to forget about the economy, and the euro bailout, to regain a bit of national pride. It's a bit of escapism, I suppose," he said.

While the Irish are looking to temporarily flee their fiscal concerns, the Poles for their part are hoping Euro 2012 will help them escape from the constraints of history. "This is basically the biggest occasion in the history of modern Poland," said Krzysztof from the tourist office. "We have for so long been defined by our communist past and before that by our time under Nazi occupation and this is now a chance to escape all that and place ourselves firmly and squarely in Europe, to prove 'we can do it'."

Pauline Clifford, 32, a civil servant with the department of health in Dublin who is in Poznan with her friend Orla Kennedy, 29, a civil servant in the department of social protection, admitted: "There's a lot we have in common.

"Poles are the biggest export to Ireland where humans are concerned," she said, adding, "and Irish people have also been Ireland's biggest export in the world, so we both, Poles and Irish, understand a lot about things like the pain of emigration, of leaving your homeland, and the whole religious heritage is also similar."

The two, clad in green T-shirts, one of which reads "Irish Dream Team", in cloud-like lettering, are staying in Niedzwiedziny – a remote settlement deep in the forests around Poznan – with a Dublin barman friend of theirs who several years ago bought an old farm house there which he's in the process of converting into a holiday house.

"It's near Gmina Skoki," says Orla, helpfully. Everyone's an expert on the local geography now.

Similar stories abound – of Polish girlfriends, Polish workmates, Polish holiday homes – and reinforce what has changed in the years since what is sometimes referred to as the "glorious odyssey" of 1988.

"Some things haven't changed: just like in 1988 we had to change currencies when we got here and there's a miserable economic backdrop, but in other ways things have changed immensely in the last 24 years," says Liam O'Neill, father of Sean.

In the darkened confines of Brogan's Bar on Szewska Street with the strains of Dirty Old Town seeping out of the juke box, Joe Bonner, 34, a town planner, his brother Donal, 30, and their friend John McElroy, also 30, both of whom have been forced to find employment outside Ireland on construction sites in Scotland and London, are enjoying pints of the Polish beer, Zywiec. Joe, whose girlfriend Monika is from Poland, can even order it in Polish. "I know the beer well. I buy it in crates from Aldi back home in Dublin," he said with a smirk. "I know I'm not being very adventurous ordering the same here, but 10 years ago if you'd asked me to name a brand of Polish beer I wouldn't have had a clue. Now I could name at least four in my sleep."

He admitted it was comical that the Polish Monika had had to stay at home finishing her masters in psychoanalysis, while he gallivanted around Poland with his mates. The three Donegal lads, who also happened to be on Donal's stag weekend, were still waiting to hear if they'd get into Sunday's match.

"Some guy called Wojtech who we've met via the internet through a friend is going to drive up from a distant part of Poland and sell us his tickets," says Joe. "I know it sounds a little crazy, but we think we can trust him to come up with the goods, and if it all goes wrong, we're sure the craic will still be mighty."